Climb in a big see through garbage bag filled with blown up colored balloons and put a big bow on your head.

Thanks to Jenny for this unique idea!

Another Idea

My idea for a great jellybeans costume is:

1 - Cut a big hole in the top of a clear trash bag.
2 - Then make to holes on each side for your arms
3 - Blow up a bunch of different color balloons, about your fist size (make sure there are different colored balloons)
4 - Tape all the balloons onto the clear plastic trash bag.
5 - After that if you want to you can put a sign on the middle of the bag saying “ Jelly Beans”